U.S. patent application number 12/661340 was filed with the patent office on 2010-09-23 for method and system for adjusting source impedance and maximizing output by rf generator.
Invention is credited to Steffan A. Benamou, David I. Brubaker, Andrew J. Hamel, David Hoffman.
Application Number | 20100241116 12/661340 |
Document ID | / |
Family ID | 42738284 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100241116 |
Kind Code |
A1 |
Benamou; Steffan A. ; et
al. |
September 23, 2010 |
Method and system for adjusting source impedance and maximizing
output by RF generator
Abstract
An electrosurgical system includes an electrosurgical probe
connected to a control console, wherein the probe is capable of
coagulating and ablating tissue depending on a selected operating
mode. Before operating the system, probe-specific data stored in a
memory device associated with the probe is read by a processing
device in the console. The data includes source impedance values
specific to a coagulation or cutting mode of operation. A constant
duty cycle value for a modulated cutting mode also is provided.
Depending on the operating mode selected, an RF generator adjusted
to have a predetermined source impedance value provides a voltage
value to the probe. During the duty-cycled mode, the RF generator
generates an instantaneous voltage value output for a duty cycle
portion that is less than 100% of a time period, which value is no
less than a maximum continuous average voltage value for the
electrosurgical probe.
Inventors: |
Benamou; Steffan A.; (San
Jose, CA) ; Hamel; Andrew J.; (San Mateo, CA)
; Hoffman; David; (Santa Cruz, CA) ; Brubaker;
David I.; (San Carlos, CA) |
Correspondence
Address: |
FLYNN, THIEL, BOUTELL & TANIS, P.C.
2026 RAMBLING ROAD
KALAMAZOO
MI
49008-1631
US
|
Family ID: |
42738284 |
Appl. No.: |
12/661340 |
Filed: |
March 16, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61210330 |
Mar 17, 2009 |
|
|
|
Current U.S.
Class: |
606/33 |
Current CPC
Class: |
A61B 2017/00973
20130101; A61B 18/1206 20130101; A61B 2018/00767 20130101; A61B
18/18 20130101; A61B 2018/00589 20130101; A61B 2018/00988 20130101;
A61B 18/148 20130101; A61B 2018/00755 20130101; A61B 2018/00779
20130101; A61B 2018/00601 20130101; A61B 2018/00702 20130101; A61B
2018/00607 20130101; A61B 18/1233 20130101; A61B 2017/00477
20130101 |
Class at
Publication: |
606/33 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Claims
1. Method of controlling source impedance of an RF generator in a
control console for an electrosurgical system including an
electrosurgical RF probe, the control console being in
communication with a memory device associated with the RF probe,
the method comprising the steps of: connecting the electrosurgical
RF probe to the control console having the RF generator, the memory
device associated with the RF probe providing probe-specific data
stored in the memory device to a processing device in the control
console, the probe data comprising at least a first source
impedance value corresponding to a coagulation operating mode for
the RF probe and a second source impedance value corresponding to a
cutting operating mode for the RF probe; selecting the coagulation
operating mode or the cutting operating mode, the processing device
operating so that the source impedance of the RF generator has a
source impedance value corresponding to the first source impedance
value when the coagulation operating mode is selected by an
operator and so that the source impedance of the RF generator has
the second source impedance value when the cutting operating mode
is selected by an operator; and operating the RF probe to coagulate
or cut tissue at a surgical site.
2. The method of claim 1, wherein the RF probe comprises a first RF
probe, and wherein at least one of the first and second source
impedance values stored in the memory device associated with the
first RF probe is different from at least one of corresponding
first and second source impedance values stored in a memory device
associated with a second RF probe.
3. The method of claim 1, wherein the probe-specific data provided
to the processing device comprises a maximum voltage average value
and a constant duty cycle value for the RF probe.
4. The method of claim 1, wherein the first source impedance value
is different than the second source impedance value.
5. Method of controlling a cutting operation for an electrosurgical
cutting system including a control console, an RF generator, and an
electrosurgical RF probe, the method comprising the steps of:
connecting the RF probe associated with a memory device to the
control console to provide probe-specific data stored in the memory
device to a processing device in the control console, the probe
data comprising a maximum continuous average voltage value and a
constant duty cycle value of less than 100% and corresponding
proportionally to a time period defined by a secondary frequency
value, the processing device having a maximum instantaneous voltage
value based on the probe data; and actuating the RF generator to
output an instantaneous voltage value in a range that is not less
than approximately the maximum average voltage value and that is
not greater than approximately the maximum instantaneous voltage
value to the RF probe to cut tissue during the constant duty cycle
value which comprises a first portion of the time period, and
wherein no voltage value is output by the RF generator or applied
to the RF probe during a second remaining portion of each said time
period.
6. The method of claim 5, wherein the step of actuating the RF
generator includes selecting application of the continuous average
voltage value having no duty cycle to the RF probe.
7. The method of claim 5, wherein the RF probe comprises a first RF
probe with a first constant duty cycle value and a second
electrosurgical RF probe different from the first RF probe is
provided having a second constant duty cycle value that is
different from the first duty cycle value of the first probe.
8. Method of controlling the operation of an RF generator disposed
in a control console of an electrosurgical system including an
electrosurgical RF probe having a memory device, the method
comprising the steps of: connecting the electrosurgical RF probe
having the memory device to the control console, a processing
device disposed in the control console for receiving probe-specific
data stored in the memory device, the probe-specific data
comprising a constant continuous coagulation voltage value, maximum
continuous average voltage value and a constant cutting duty cycle
value for operating the probe in a cutting operating mode, the
processing device provided with a maximum instantaneous voltage
value related to the maximum continuous average voltage value and a
constant duty cycle value; selecting a coagulation operating mode
or the cutting operating mode, wherein in the cutting operating
mode the operator selects a continuous cutting mode or a modulated
cutting mode, wherein in the modulated cutting mode the RF
generator intermittently outputs to the RF probe an instantaneous
voltage value that is no less than the maximum continuous average
voltage value and no more than the maximum instantaneous voltage
value, the constant cutting duty cycle value being defined as a
percent value that is less than 100%, and wherein the instantaneous
voltage value is applied to the probe during the constant cutting
duty cycle value of a time period that is defined by the inverse of
a first secondary frequency value, the intermittent application of
the instantaneous voltage value enabling cutting of tissue, and
wherein in the coagulation operating mode the RF generator outputs
the constant continuous coagulation voltage value for obtaining a
desired coagulation effect; and operating the electrosurgical
system to coagulate or cut tissue at a surgical site.
9. The method of claim 8, wherein the probe specific data further
comprises a constant coagulation duty cycle value for a period
defined by the inverse of a second secondary frequency value, that
is provided to the processing device for operating the RF generator
in a modulated coagulation mode.
10. The method of claim 9, wherein connecting the RF probe to the
control console comprises connecting a cable of the RF probe to a
single RF cable port on the control console to supply power to the
RF probe.
11. The method of claim 9, wherein the first secondary frequency
value and the second secondary frequency value are equal and are
stored in the processing device, and wherein the cutting duty cycle
value is different than the coagulation duty cycle value.
12. The method of claim 8, wherein the probe-specific data further
comprises the maximum instantaneous voltage value, a coagulation
source impedance value for the RF generator in the coagulation
operating mode and the probe-specific data further comprises a
cutting source impedance value for the RF generator in the cutting
operating mode.
13. The method of claim 12, wherein the step of selecting the
coagulation operating mode or the cutting operating mode comprises
providing the RF generator with the coagulation source impedance
value from the processing device in the control console when the
coagulation operating mode is selected by an operator, and
providing the RF generator with the cutting source impedance value
from the processing device in the control console when the cutting
operating mode is selected by an operator, the coagulation source
impedance value being different than the cutting source impedance
value.
14. An electrosurgical system, comprising: a control console having
a processing device disposed therein; an electrosurgical probe that
detachably connects to the control console; an RF generator for
generating a voltage value for energizing the electrosurgical
probe; and a memory device associated with the RF probe, the memory
device storing probe-specific operating parameters including a
cutting duty cycle value for a cutting mode, wherein the processing
device obtains the probe-specific parameters from the memory device
and after selection of the cutting mode, the processing device
controls the RF generator to output an instantaneous voltage value
for the constant cutting duty cycle portion of each time period
defined by the inverse of a secondary frequency, wherein the
instantaneous voltage value is intentionally greater than a maximum
average voltage value.
15. The electrosurgical system of claim 14, wherein the
instantaneous voltage value is more than the maximum average
voltage value/cutting duty cycle value, whereby the instantaneous
voltage value applied to the RF probe exceeds the maximum average
voltage value.
16. The electrosurgical system of claim 14, wherein the secondary
frequency value is stored in the processing device.
17. The electrosurgical system of claim 14, wherein the
probe-specific operating parameters stored in the memory device
include a coagulation duty cycle value for a modulated coagulation
mode, the parameters being obtained by the processing device so
that in operation, after selection of the coagulation mode having a
coagulation duty cycle value instead of no duty cycle, the
processing device controls the RF generator to output an
instantaneous coagulation voltage value for a constant coagulation
duty cycle portion that is less than 100% of each time period
defined by the inverse of the secondary frequency.
18. The electrosurgical system of claim 17, wherein the
probe-specific operating parameters stored in the memory device
comprise source impedance values including a first source impedance
value for the RF generator in the coagulation mode and a second
source impedance value for the RF generator in the cutting
mode.
19. The electrosurgical system of claim 14, wherein the
probe-specific operating parameters stored in the memory device
comprise a first source impedance value for the RF generator in a
coagulation mode and a second source impedance value for the RF
generator in the cutting mode.
20. The electrosurgical system according to claim 19, wherein the
first source impedance value is different than the second source
impedance value.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/210,330, filed Mar. 17, 2009, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention is related generally to an electrosurgical
system having an RF generator with a variable source impedance for
providing a maximum RF power value to an RF probe, and having a
cutting duty cycle value that provides increased instantaneous
voltage to the probe for cutting tissue.
BACKGROUND OF THE INVENTION
[0003] Endoscopy in the medical field allows internal features of
the body of a patient to be viewed without the use of traditional,
fully-invasive surgery. Endoscopic imaging systems enable a user to
view a surgical site and endoscopic cutting tools enable
non-invasive surgery at the site. For instance, an RF generator
provides energy to a distal end tip of an RF probe within the
surgical site. In one mode, the RF probe provides RF energy at a
power level to ablate or otherwise surgically remove tissue. In
another instance, RF energy is provided to the RF probe in order to
coagulate the tissue at the surgical site to minimize bleeding
thereat.
[0004] Tissue ablation is achieved when a high power electrical
signal having a sufficiently large voltage is generated by the
control console and directed to the attached probe. Application of
the high power signal to the probe results in a large voltage
difference between the two electrodes located at the tip of the
probe (presuming a bipolar probe), with the active electrode being
generally 200 volts more than the passive or return electrode. This
large voltage difference leads to the formation of an ionized
region between the two electrodes, establishing a high energy field
at the tip of the probe. Applying the tip of the probe to organic
tissue leads to a rapid rise in the internal temperature of the
cells making up the neighboring tissue. This rapid rise in
temperature near instantaneously causes the intracellular water to
boil and the cells to burst and vaporize, a process otherwise known
as tissue ablation. An electrosurgical "cut" is thus made by the
path of disrupted cells that are ablated by the extremely hot, high
energy ionized region maintained at the tip of the probe. An added
benefit of electrosurgical cuts is that they cause relatively
little bleeding, which is the result of dissipation of heat to the
tissue at the margins of the cut that produces a zone of
coagulation along the cut edge.
[0005] In contrast to tissue ablation, the application of a low
power electrical signal having a relatively low voltage to the
active electrode located at the tip of the probe results in
coagulation. Specifically, the lower voltage difference established
between the active and return electrodes results in a relatively
slow heating of the cells, which in turn causes desiccation or
dehydration of the tissue without causing the cells to burst.
[0006] Basic operation of an electrosurgical system can be analyzed
in view of at least two relationships.
[0007] The first relationship is described by Ohm's law, which in
simplest terms, is represented by the equation V=IxR or
alternatively V=(IxZ), where:
[0008] I=electrical current;
[0009] R=resistance or impedance to the current (hereafter referred
to as Impedance (Z), which includes capacitive and inductive
loading); and
[0010] V=voltage or force that "pushes" the current through the
impedance.
[0011] The second relationship is the definition of power (P),
which can be calculated by the equation (P=IxV). The resultant
product of current I and voltage V represents the amount of energy
that is transferred within a defined period of time.
[0012] FIGS. 1 and 2 correspond to FIGS. 1 and 2 of U.S. Patent
Publication 2007/0167941, the disclosure of which is hereby
incorporated by reference.
[0013] As illustrated in FIG. 1, a typical electrosurgical system
10 includes an electrosurgical probe 12 (hereafter referred to
simply as "probe") and a control console or controller 14. The
probe 12 generally comprises an elongated shaft 16 with a handle 18
at one end and a tip 20 at the opposite end. A single active
electrode 19 is provided at the tip 20 if the probe 12 is of a
"monopolar" design. Conversely, the probe 12 may be provided with
both an active electrode 19 and a return electrode 21 at the tip 20
if the probe is "bipolar" in design. The probe 12 connects to
control console 14 by means of a detachable cable 22. The current
for energizing the probe 12 comes from control console 14. When
actuated, the control console 14 generates a power signal suitable
for applying across the electrode(s) located at the tip 20 of the
probe 12. Specifically, current generated by the control console 14
travels through the cable 22 and down the shaft 16 to tip 20, where
the current subsequently energizes the active electrode 19. If the
probe 12 is monopolar, the current will depart from tip 20 and
travel through the patient's body to a remote return electrode,
such as a grounding pad. If the probe 12 is bipolar, the current
will primarily pass from the active electrode 19 located at tip 20
to the return electrode 21, also located at tip 20, and
subsequently along a return path back up the shaft 16 and through
the detachable cable 22 to the control console 14.
[0014] Configuration of the control console 14 is carried out by
means of an interface 15, while actuation and control of the probe
12 by the surgeon is accomplished by one or more switches 23,
typically located on the probe 12. One or more remote controllers,
such as, for example, a footswitch 24 having additional switches 26
and 28, respectively, may also be utilized to provide the surgeon
with greater control over the system 10. In response to the
surgeon's manipulation of the various switches on the probe 12
and/or remote footswitch 24, the control console 14 generates and
applies either a low power signal or high power signal to probe 12.
As will be discussed in greater detail below, application of a low
power signal to probe 12 results in coagulation of the tissue
adjacent the tip 20 of the probe 12. In contrast, application of a
high energy signal to probe 12 results in tissue ablation.
[0015] While operating in coagulation mode, the control console 14
of the prior art system shown in FIG. 1 is configured to drive the
attached probe at a low, but constant, power level. Due to inherent
varying conditions in tissue (i.e., the presence of connective
tissue verses fatty tissue, as well as the presence or absence of
saline solution), the impedance or load that the system experiences
may vary. According to Ohm's law, a change in impedance will result
in a change in current levels and/or a change in voltage levels,
which in turn, will result in changing power levels. If the
operating power level of the system changes by more than a
predefined amount, the control console will attempt to compensate
and return the power back to its originally designated level by
regulating either the voltage and/or current of the power signal
being generated by the console and used to drive the attached
probe.
[0016] While operating in tissue ablation mode, the control console
of the system shown in FIG. 1 is configured to drive the attached
probe at as high a power level as possible without exceeding a
maximum average power level, which in some instances may equal 400
watts.
[0017] The electrosurgical system shown in FIG. 1 modulates the
entire power supply signal as a whole, turning the signal on and
off in a manner similar to a pulse width modulated (PWM) signal.
Furthermore, the power signal is dynamically modulated on and off
so as to behave like a PWM signal having a variable duty cycle. As
a result, the percentage of time that the power signal is "on",
compared to the percentage of time that the signal is "off", will
vary depending on the percentage of time that the power levels of
the signal exceed the maximum limit over a predetermined interval
of time.
[0018] Consequently, the duty cycle of the power signal is
dynamically modulated so that even though the power levels of the
signal may briefly exceed the maximum power limit for a portion of
time during a specified interval, the average power level over that
interval of time remains acceptable.
[0019] To further illustrate the above point, FIG. 2 depicts
several examples of high frequency power signals generated by the
control console 14 over a 20 millisecond period of time and used to
drive the attached probe 12. Signal A is a power signal in the form
of a 200 KHz sine wave. No modulation of signal A is present with
respect to a signal duty cycle, resulting in a power signal that is
continuously on (i.e., 100% duty cycle) for the entire 20
millisecond duration.
[0020] In FIG. 2, signal B is similar to signal A, but has been
briefly modulated roughly half-way through the 20 millisecond
period. In this instance, for example, changing environmental
variables may have resulted in the power level of the signal
briefly exceeding an established maximum limit during the previous
20 millisecond period (not shown). To compensate for this prior
spike in power level and assure that the average power of the
signal does not exceed a maximum limit, the system briefly
modulates signal B during the next 20 millisecond period (shown),
effectively turning the signal off for a moment. Thus, for example,
signal B is modulated or turned off for approximately 5
milliseconds during the 20 millisecond period depicted, resulting
in the signal effectively having a 75% duty cycle for the period
shown.
[0021] To compensate for power level spikes that are larger in
magnitude or longer in duration, the system dynamically modulates
the duty cycle of the power signal during the next monitoring
interval to effectively turn off the signal for a longer period of
time. For example, signal C of FIG. 2 is similar to signal B, but
is modulated to have a lower duty cycle, resulting in signal C
being turned off for a longer period of time during the 20
millisecond interval shown.
[0022] By dynamically adjusting a duty cycle of the power signal,
the average power of the signal can be maintained below an
established maximum power limit. Furthermore, it has been observed
that the ionized high energy field maintained at the tip of the
probe 12 does not collapse, but remains stable, if the effective
duty cycle of the power signal is modulated quickly enough (i.e.,
turning the signal on or off in increments of 50 milliseconds over
a 1 second period).
[0023] In the electrosurgical system 10 illustrated in FIG. 1
above, the duty cycle is varied for the waveform only in instances
where the voltage or current causes the power value of the RF probe
to exceed the acceptable power value. Thus, in the prior art, the
duty cycle is varied by differing amounts, as necessary, to account
for unintended increases in power value beyond the average power
value of the system.
[0024] A non-volatile memory device (not shown) and reader/writer
(not shown) can be incorporated into the body 18 of the probe 12,
or alternatively, incorporated into or on the cable 22 that is part
of the attachable probe and which is used to connect the probe 12
to the control console 14 of the system. Alternatively, the memory
device may be configured so as to be incorporated into or on the
communication port that is located at the free end of the cable 22
and which is used to interface the cable with a corresponding port
on the controller 14.
[0025] During manufacturing of the attachable probe shown in FIG.
1, data representing probe-specific operating parameters is loaded
into the memory device. Upon connection of the attachable probe 12
to the control console 14 of the system 10, the data stored in the
probe's non-volatile memory can be accessed by the reader and
forwarded on to the controller 14. As such, once a probe 12 is
connected, the controller 14 accesses the configuration data of the
specific probe 12 and automatically configures itself based on the
operating parameters of the probe 12.
[0026] Beyond probe-specific operating parameters, the prior art
memory device within each attachable probe 12 can store additional
data concerning usage of the probe 12. This usage data can comprise
a variety of information. For example, usage data may represent the
number of times a probe 12 has been used, or the duration of the
time that the probe has been activated overall or at different
power levels. Additional usage data may restrict the amount of time
that a specific attachable probe can be used. Alternatively, a
probe 12 may be programmed so it can only be used for a limited
duration of time starting from the moment the probe was first
attached to a control console and powered up. For example, a probe
may be programmed to that it only functions for a 24-hour period
starting from when the probe is first activated. Based on a clock
maintained within the control console, a time stamp is written to
the memory device of the probe when the probe is attached to the
console for the first time and powered up. Any later attempted use
of that probe will trigger a comparison of the stored time stamp to
the current time reported by the control console, and if the
allotted amount of time has already passed, the system will not
allow the probe to be used.
[0027] Alternatively, a specific prior art probe is dynamically
restricted, so that the overall amount of time allocated for use of
the probe will vary depending not only on the amount of time the
probe has been used, but also the power levels that the probe was
driven at during its use. As such, a specific attachable probe may
be limited to 1 hour of use if always driven at a maximum power,
but may be usable for 3 hours if all prior uses occurred at
substantially lower power levels.
[0028] In addition to usage data, the prior art memory device can
store information concerning any errors that were encountered
during use of the probe 12. For example, the failure of a probe to
activate would lead the control console 14 to issue and store one
or more error codes into the probe memory. Technicians can later
retrieve these error codes to aid in their examination of the
failure.
[0029] In addition to probe-specific operating parameters and usage
data, the memory device incorporated into each probe may also be
programmed by the manufacturer to include software scripts or
updates for the control console of the system.
[0030] In the electrosurgical system illustrated in FIG. 1, the
power output from control console 14 has a constant source
impedance regardless of the probe utilized or the mode of
operation.
[0031] As discussed above, the electrosurgical system 10 shown in
FIG. 1 provides a modulated duty cycle power output only to
decrease power output in instances where the power exceeds the
desired power due to incidental variations in the impedance of the
load or other power control issues. Further, the duty cycle value
varies depending on the amount that the power exceeds the desired
average power level. Thus, during normal operation, the output
power value may, in some instances, not exceed the desired intended
constant average power value resulting in no duty cycle variations
in the power output by an energy generator.
[0032] The present invention is directed to improving cutting or
coagulation of tissue by an RF probe, such as by optimizing power
delivery to tissue by adjusting the source impedance value of an RF
generator.
[0033] In one embodiment of the invention, information regarding
source impedance values for an RF generator is stored on an RF
probe and read by a processing device. The processing device
controls the source impedance value of the RF generator based on
the stored values to optimize power transfer from the RF generator
to tissue via the RF probe.
[0034] In another embodiment of the invention, improved operation
of an electrosurgical system is obtained by duty cycling of voltage
output from a RF generator to increase the instantaneous voltage
value applied to an RF probe. The duty cycling information is read
from a memory device on the RF probe. Modulating the RF voltage
value at a secondary frequency with a duty cycle of less than 100%
reinitiates a voltage arc dynamically on different tissues at the
beginning of each time period that includes the duty cycle value.
Periodically reinitiating arcing by duty cycling the RF output
voltage value helps to maintain consistent burn characteristics on
various tissues. Also, constant duty cycling tends to physically
push tissue away from the probe tip during ablation to maintain
good spacing between the probe tip and tissue, which creates
optimal arcing, and thus helps to prevent clogging. Further, the
duty cycling of output voltage helps to control depth of necrosis
because the heated tissue is allowed to thermally relax between
each duty cycle application of RF voltage.
[0035] Another advantage of the invention is that the duty cycle
applied to the RF voltage output decreases the amount of total time
the probe is exposed to high RF voltage, which reduces probe
degradation as compared to a continuous application of RF power. In
this embodiment, cyclically applying voltage to the RF probe at
less than the maximum allowable voltage value, or even at the same
voltage value as a non-duty cycled RF generator output, reduces
heating of the surgical site, such as a joint, without
significantly affecting cutting performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 depicts an electrosurgical system that includes an
electrosurgical probe connected to a control console, along with a
footswitch.
[0037] FIG. 2 depicts examples of high frequency RF signals
generated by the control console shown in FIG. 1 for driving the
attached probe.
[0038] FIG. 3 depicts an electrosurgical system of the invention
that includes a footswitch, an electrosurgical probe and a powered
surgical handpiece for attachment to a control console.
[0039] FIG. 4 is a block diagram illustrating components of the
control console and the powered handpiece of FIG. 3.
[0040] FIG. 5 illustrates a graph showing delivered power versus
load impedance for a number of different source impedances of an RF
generator.
[0041] FIG. 6 is a flowchart showing steps for configuring of an RF
generator with a predetermined source impedance value depending on
selected operating modes.
[0042] FIG. 7 is a graph illustrating a normal RF waveform and a
duty cycled RF waveform.
[0043] FIG. 8 is a flowchart showing selection of a continuous
operation or duty cycled operation of an RF generator after
selection of a coagulation or cutting mode.
DETAILED DESCRIPTION
[0044] FIG. 3 shows a surgical system 30 including a console 32
having a footswitch receiving port 34, a handpiece receiving port
36 and a RF probe receiving port 38. The footswitch receiving port
34 provides a connection to the control console 32 for a footswitch
40. Handpiece receiving port 36 receives the connection jack of a
powered surgical handpiece 42 with a cutting element or burr 43
attached thereto. One conventional handpiece is disclosed in U.S.
Patent Publication No. 2003/0093103, the disclosure of which is
hereby incorporated by reference herein. RF probe receiving port 38
receives a connecting jack of an RF probe 44.
[0045] As shown in FIG. 4, the powered handpiece 42 of the surgical
system 30 includes an antenna 46. In one embodiment, a non-volatile
memory device, such as an RFID chip 48, is provided in the cutting
element 43. A transceiver 47 located in the control console 32 is
connected to the antenna 46 for reading probe-specific data.
Antenna 46 carries power from the transceiver 47 to the RFID chip
48 in the cutter element 43 and returns data from the chip to the
transceiver. In some embodiments, the transceiver 47 also writes
data to the RFID chip 48.
[0046] One embodiment of the RF probe 44 generally corresponds to
the probe structure illustrated in FIG. 1, except additional
probe-specific data, described later herein, is provided on a
one-wire memory device and provided to the control console 32. The
console 32 includes a processing device 50 for processing the data
received from the one-wire memory device. The processing device 50
controls an RF generator 52 that provides RF energy to the RF probe
44 to power an electrode 54 at the distal end thereof. In one
embodiment, the RF probe 44 and the electrode 54 form a disposable
unit.
[0047] The embodiments of FIGS. 3 and 4 include the powered
handpiece receiving port 36 that enables the control console 32 to
provide power to surgical handpiece 42. The surgical handpiece 42
enables mechanical cutting and debridement of bone and soft
tissue.
RF Generator Source Impedance
[0048] FIG. 5 shows a graph plotting power delivered (watts) versus
load impedance Z.sub.L (ohms) for a single electrosurgical probe.
The graph shows power delivered values versus load impedance values
for five different RF generator source impedances Z.sub.source as
represented by respective plotted lines on the graph. The source
impedance values Z.sub.source are 200.OMEGA., 225.OMEGA.,
250.OMEGA., 275.OMEGA. and 300.OMEGA..
[0049] In general, when the load impedance is low, the power
delivered is low to prevent a large current from passing through
the electrode 54. Such a large current may cause electric shock or
other dangerous conditions and thus is prevented by current
limiting circuitry in the RF generator 52.
[0050] Different RF probes 44, due to their shape, size or other
factors, result in different load impedances Z.sub.L provided to
the console for the same tissue type or tissue characteristics.
Thus the RF generator 52 may provide optimal delivered power for
the RF probes, as shown in FIG. 5, by adjusting the source
impedance.
[0051] The load impedance value Z.sub.L is also affected greatly by
whether the tissue is being cut or the tissue is being coagulated.
Further, the temperature of the joint being operated on and the
amount of fluid in the joint also can affect the load impedance
value Z.sub.L.
[0052] Since various RF probes 44 are intended for use in various
surgical operations, the load impedance range of use for cutting is
predictable. Thus, the source impedance value Z.sub.source that
provides the highest delivered power in the expected load impedance
range is stored in the RFID memory chip 48 and is provided to the
processing device 50. Therefore, different source impedance values
Z.sub.source are provided for various different RF probes 44
depending on the probe structure and the intended use of the
probe.
[0053] In some embodiments, the RFID chip 48 includes one or more
values for the source impedance of the RF generator 52 for use with
the particular probe. For instance, one source impedance value,
such as 200.OMEGA., may be provided for a coagulation operation and
another source impedance value, such as 250.OMEGA., may be provided
for the RF generator 52 when the RF probe 44 is utilized for
cutting tissue or ablation.
[0054] Operation of one embodiment of a surgical system 30 having
dynamic source impedance values Z.sub.source is illustrated in FIG.
6. At step 60, the jack or connector of the RF probe 44 is inserted
into the corresponding probe receiving port 38 on the control
console 32. Then, at step 62, the processing device 50 of the
console 32 automatically receives the probe data stored in the RFID
chip 48. The probe data includes RF generator source impedance
values Z.sub.source for different operating conditions of the
specific RF probe 44. At step 64, the user then selects either a
cutting mode or a coagulation mode. If a coagulation mode is
selected, the processing device 50 advances to step 66. At step 66,
the processing device 50 operates on circuitry within the control
console 32 to provide a stored coagulation source impedance value
Z.sub.source to the RF generator 52 for the coagulation mode. Then,
at step 70, the processing device 50 returns to a control mode
wherein the RF generator 52 is selectively controlled by a user to
apply RF energy and coagulate tissue or veins.
[0055] If the cutting mode is selected at decision step 64, the
processing device 50 advances to step 68. At step 68, the
processing device 50 controls circuitry so that the RF generator 52
is provided with a cutting source impedance value Z.sub.source that
was previously read by the processing device 50 from the RFID chip
48. Therefore, as illustrated in FIG. 6, in operation, the RF
generator 52 is provided with a source impedance value Z.sub.source
that maximizes the power delivered during operation of the RF probe
44 in either operating mode.
Increasing Instantaneous Power
[0056] As discussed above, in many surgical devices the maximum
amount of power mandated for use with a probe is 400 watts per
second. Some embodiments of the invention provide a greater
instantaneous power to tissue while maintaining the overall
specified average power of, for example, 400 watts/second. Some
embodiments provide RF power to the probe 44 at a specified
predetermined constant duty cycle of a time period T defined by a
secondary frequency value f that is less than the RF frequency.
Specifically, time period T is the inverse of the frequency f and
thus equals 1/f. Therefore, instantaneous power delivered can be
increased without exceeding a maximum total power requirement for a
given time period.
[0057] This approach for increasing the instantaneous power is
described by the equation set forth below.
P.sub.inst=P.sub.ave/duty cycle %
[0058] In the above equation, P.sub.ave is P an average constant
continuous power value that provides maximum allowable power to an
electrosurgical probe, such as 400 watts per second. P.sub.inst is
a maximum instantaneous power value greater than the constant
continuous average power P.sub.ave. P.sub.inst is determined by
P.sub.ave and a duty cycle percent value. The smaller the duty
cycle value, the greater the value for P.sub.inst.
[0059] In FIG. 7, a normal RF waveform has a constant voltage value
Vnom, which at a constant load impedance value Z.sub.1, provides a
constant average power value P.sub.ave. Thus, after the beginning
start-up of voltage applied to the RF probe 44, nominal voltage
V.sub.nom is applied continuously, to obtain the constant average
power value P.sub.ave for the entirety of the illustrated normal RF
waveform.
[0060] An improvement in power applied to an RF probe 44, at least
under certain conditions, is illustrated by the duty cycled RF
waveform also shown in FIG. 7. As discussed above, the duty cycled
waveform has a time period T that is defined by the inverse of the
secondary frequency value f. As discussed above, the secondary
frequency value f must be much less than the RF frequency value
applied to the RF probe 44. The secondary frequency value, in some
embodiments, has a value of 20 Hz.
[0061] The over voltage value V.sub.ov shown in FIG. 7 at a
constant load impedance value Z.sub.L provides the instantaneous
maximum power value P.sub.inst described above. The over voltage
value V.sub.ov is greater than the voltage value V.sub.nom as a
result of the off portion t.sub.off of each time period T. Thus,
voltage value V.sub.ov shown in FIG. 7 and applied to RF probe 44
by the RF generator 52 results in an instantaneous power value
P.sub.inst that is greater than a corresponding average power value
P.sub.ave even though total power over time periods T is about the
same.
[0062] In FIG. 7, the duty cycle t.sub.on is approximately 75% of
the period T and the off portion t.sub.off is approximately 25% of
the time period T. If the constant duty cycle were decreased from
75% to 50% in another embodiment, the over voltage value V.sub.ov
applied for each duty cycle would then increase resulting in an
increase in the instantaneous power value P.sub.inst as set forth
in the above power equation. Again, the embodiment illustrated in
FIG. 7 is plotted with the load impedance value Z.sub.L having a
constant value for the entirety of the time illustrated along the
length of the x-axis.
[0063] If there are changes in load impedance Z.sub.L along the
time axis shown in FIG. 7 for the duty cycled RF waveform, the
overvoltage value V.sub.ov generally is maintained and thus the
instantaneous power value P.sub.inst for the duty cycle t.sub.on of
each time period T may vary slightly. Thus the Z.sub.source value
must be as close as possible to Z.sub.Load to maximize power output
from the RF probe 44.
[0064] As in the source impedance embodiment discussed above,
maximum power and duty cycle control information can be stored in
the memory device, along with other RF probe data, as well as
source impedance values Z.sub.source.
[0065] Operation of the RF probe 44 in the instantaneous increased
power arrangement having a duty cycled RF waveform is explained in
the flow chart of FIG. 8. In step 78 of FIG. 8, the RF probe 44 is
plugged into the RF probe receiving port 38. At step 80,
probe-specific data is read from the memory device by the
processing device 50. In some embodiments, probe data read by the
processing device 50 disposed in the console 32 includes
probe-specific duty cycle values for both coagulation modes and cut
modes. In some embodiments, a secondary frequency value is also
provided. In some embodiments, a probe-specific constant voltage
value for a continuous coagulation mode can be provided.
[0066] At decision step 82, the user selects either the coagulation
mode or the cutting mode. If the cutting mode is selected, the
processing device 50 advances to decision step 84. At decision step
84, a user selects between cutting with a duty cycle or operating
at a continuous voltage cut value. If the user selects operation at
a continuous voltage value, the processor 50 advances to step 86
and in view of the probe data controls the RF generator 52 to
output the non-duty cycle maximum average voltage V.sub.nom. Then,
at step 88, the processing device 50 returns to enable powering of
the RF generator 52 by a user at the continuous voltage cut value,
corresponding to the maximum average power value P.sub.ave.
[0067] If the operator decides to cut tissue with a duty cycle
arrangement at step 84, the processing device 50 advances to step
90. At step 90, the processor device 50 calculates instantaneous
power value P.sub.inst from the stored duty cycle percentage value
read from the memory device and the average power value P.sub.ave.
The processor device 50 then calculates an expected over voltage
value V.sub.ov that is intended to result in the instantaneous
power value P.sub.inst during the duty cycle. The processing device
50 then advances to step 92 and returns to enable operation in the
duty cycled cutting mode.
[0068] Returning to step 82, if the operator selects the
coagulation mode, the processing device 50 advances to decision
step 94. At decision step 94, if the user selects operating the RF
probe 44 at a continuous coagulation power value, the processor
device 50 advances to step 96 and configures or controls the RF
generator 52 for operation at an essentially constant continuous
voltage value that coagulates tissue and then returns at step 88 to
permit operation of the RF probe 44.
[0069] At decision step 94, if the user decides to perform
coagulation with a duty cycled value, the processing device 50
advances to step 98. At step 98, a coagulation duty cycle power
value is obtained by dividing the average desired coagulation power
value by a duty cycle value received by the processing device 50
from the memory device. The instantaneous power value is then
converted to a coagulation operating voltage and output by the RF
generator 52 for the duty cycle t.sub.on of the time period T.
[0070] As with the above embodiments directed to RF generator
source impedance values Z.sub.source discussed above, in these
additional embodiments the secondary frequency value f, and
especially the stored duty cycle values may vary for different
types of probes and may also vary for the coagulation mode and the
cutting mode for any given RF probe. In other embodiments, the
secondary frequency value f is a constant value for all RF probes
and is stored in the processing device 50.
[0071] While FIG. 8 shows manual selection of a continuous
essentially constant voltage value or of a duty cycled voltage
value provided to an RF probe 44, in another embodiment a duty
cycled power value is output from the RF probe automatically in the
coagulation mode. In other embodiments, a continuous constant
voltage is output by the RF generator in every instance that the
coagulation mode is selected.
[0072] While FIG. 8 does not show the selection of a source
impedance value, the value Z.sub.source can be provided to control
the RF generator 52 along with the stored duty cycle value at step
90 or at step 98.
[0073] While the disposable RF probe 44 is disclosed as having a
I-line memory device or an RFID chip, other non-volatile memory
devices are also contemplated.
[0074] In another embodiment of the invention, the normal nominal
voltage value V.sub.nom illustrated in FIG. 7 for a continuous
mode, operates as an RF generator 52 output voltage value V.sub.nom
during on periods t.sub.on of a duty cycle. This embodiment has an
improved cooling effect on the tissue and arc reinitiation provides
a desired cutting effect despite a lesser amount of voltage being
applied to the tissue over time period T.
[0075] In another embodiment of the invention, a voltage value
between V.sub.nom and V.sub.ov having a duty cycle is applied to
the RF probe 44. This voltage value, determined by the processor
device 50, maximizes performance by providing cooling during time
t.sub.off while providing a voltage value greater than or equal to
V.sub.nom during t.sub.on.
[0076] In another embodiment of the invention, a blend mode
providing simultaneous cutting and coagulation of tissue may be
provided by the RF generator 52. In this arrangement, a specific
source impedance value that is different from the source impedance
value for other modes is contemplated.
[0077] In some embodiments, the RF probe 44 has a bipolar electrode
and in other embodiments the RF probe has a monopolar
electrode.
[0078] In some embodiments, the handpiece structure of the RF probe
44 is not disposable. In these embodiments the electrode 54
projecting from the distal end of the probe body is detachably
coupled to the probe body.
[0079] Although particular preferred embodiments of the invention
are disclosed in detail for illustrative purposes, it will be
recognized that variations or modifications of the disclosed
apparatus, including the rearrangements of parts, lie within the
scope of the present invention.
* * * * *